Field of the Invention
The present invention relates to a matrix key input interface that enables detection of an earth fault on a key common signal line and a key data signal line.
Description of the Related Art
A key matrix circuit is conventionally known which acquires key information by scanning information on keys each connected to a grid-like wiring pattern on a column-by-column basis. Compared to a configuration in which the keys are connected to the respective wiring patterns on a one-to-one basis, such a key matrix circuit, including the wiring pattern arranged like a grid, enables information on many keys to be detected using a small number of signal lines.
However, if an earth fault occurs in the wirings between the key matrix circuit and a common signal output circuit or a data signal reception circuit (hereinafter referred to as an LSI), an input different from a desired input signal may be detected, leading to a malfunction.
Japanese Patent Application Laid-Open No. 61-58025 discloses a conventional technique relating to a key matrix circuit having a function to detect an abnormality in an input so as to prevent a malfunction of the relevant equipment.
The conventional key matrix circuit includes no mechanism that detects an earth fault in the wirings between the key matrix circuit and the LSI. Thus, when an earth fault occurs in the wirings, an input different from the desired input signal may be detected, leading to a malfunction.
Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 61-58025, mentioned above, detects an abnormality in the input to the key matrix circuit but does not detect an earth fault in the wirings between the key matrix circuit and the LSI.